Patent GB-1082656-A (GB)
Title: Improvements in or relating to pneumatic control systems
Inventor: GOVAN WILLIAM LIVINGSTON
IPC: G05B11/58
Filed: 1965-04-29
Abstract: 1,082,656. Extruding. FARREL CORPORATION. April 29, 1965, No. 18071/65. Heading B3P. [Also in Divisions F1 and G3] The output of a variable-delivery pump is controlled by a pneumatic control system which provides a plurality of control points. The pump is an hydraulic pump and is used to supply an extrusion press, which may be used for sheathing cables withlead or aluminium. The press ram 18, Fig. 4 (not shown), is mounted on a crosshead 18a actuated by a main piston 20 and side pistons 24 which effect a quick approach stroke and also retract the ram; the pistons 24 may also assist during extrusion. A pre-fill valve 21 is fitted. Limit switches such as 57, 63, 74 are actuated by the crosshead to initiate various steps in the extrusion cycle. The press has an hydraulic billet loader 82, Fig. 2 (not shown), a die slide assembly 89 actuated by an hydraulic cylinder 91 and a shear assembly 88, Fig. 1 (not shown), actuated by an hydraulic cylinder 88. Billet container 85 is movable axially along inclined guides 83, Fig. 3 (not shown), by hydraulic cylinders 87, Fig. 2 (not shown). Hydraulic fluid for operation of the rams is supplied by two reversible variable displacement radial cylinder pumps 1, 2, Fig. 4 (not shown), through solenoidactuated valves 8-13 controlled by the limit switches such as 57, 63, 74, and an hydraulicpressure switch 69. An electrical control circuit is described, Figs. 10A, 10B (not shown), which provides automatic cycling or manual control from a pulpit 36a, Fig. 1 (not shown). The pump delivery is controlled by a pneumatic system, Fig. 5 (not shown). The invention may be applied to the control of the hydraulic cylinder for the die slide, billet loader, shear and container. The shear may be operated by one of the pumps whilst the ram is retracted by the other pump. Hydraulic pumps.-The pumps 1, 2 are driven by motors 3, Fig. 2 (not shown), through flexible couplings 92. Each pump comprises a pintle 96, Fig. 6 (not shown), radial pistons 97, rotor 98 and a slide block 99 which is moved by differentially-acting hydraulic pistons 105, 102, Fig. 7 (not shown), for varying or reversing the pump output. The control cylinders 104, 103 are supplied from a gear pump with pressure liquid which acts continuously on piston 104 and is fed into cylinder 103 under control of a valve spool 107 surrounded by a sleeve 108 connected to the piston 102 for performing a follow-up movement. Valve spool 107 is actuated by a pneumatic piston 111 biased to the left by a spring 113 supplemented if necessary by uniform air pressure, and movable to the right by signal air pressure admitted to cylinder 110 from the pneumatic control system, Fig. 5 (not shown). Pneumatic control system.-The pumps 1, 2, Fig. 5 (not shown), are regulated by pneumatic control means 56, 45 to which signal air is supplied through solenoid-actuated spring- biased valves. High-pressure signals produce maximum output at ports b feeding hydraulic pressure line 6 for forward ram movement; low-pressure signals produce maximum output at ports a for reverse movement. The system includes a basic supply regulator 28, manuallyoperated regulators such as 34, 36 which provide alternative control points, and an idling pressure regulator 32. To compensate for slippage which occurs at high ram pressures, a pressure transducer 50 and computer 49 are incorporated in the pneumatic system. Transducer 50, Fig. 8 (not shown), comprises a measuring element 116 connected to the main hydraulic pressure line 6, Fig. 4 (not shown), and which actuates through linkage 117, 118 a flap valve 119 controlling air discharge from a nozzle 120. This controls through duct 129 and diaphragm 126, a valve 133 which regulates the air supply from input 31 to output line 131 leading to the computor 49. A bellows 121 connected to the output line provides a followup for the nozzle 120. The computer, Fig. 9 (not shown) comprises bellows 122b connected to the transducer, bellows 138b connected to constant air pressure, bellows 44b connected to the signal air pressure line 44 and a bellows 53b connected to an output line 53. The bellows assembly actuates a flap valve 139 which is rockable about adjustable pivots 140 to control air discharge from a nozzle 141 which in turn controls a valve 142 between an air supply line 31 and the output line 53. Pressure in the output line acts on bellows 53b to provide a follow-up.